1. Field of the Invention
The present invention relates to a water storage structure composed of a collection of small objects having properties of repelling water or the like.
2. Description of the Background Art
The world's population, which was 1.5 billion at the beginning of the 20th century, has exceeded 6 billion in the 21st century. The increase rate will not fall and the world's population will reach 9 billion at 2050, and thus the earth will have a population that is six times as much as that at the beginning of the 20th century. Meanwhile, the desert, which is unsuitable for cropland, occupies 30% of the land of the earth, further desertification of cropland has occurred, and thus the cropland tends to decrease.
If plants can be grown in the desert, improvement of the land gradually progresses from the plants, and the number and kinds of plants that grow can be increased. First, for a barren land, it is necessary to build ground conditions under which plants continue to live. The most essential thing as a condition under which plants continue to live in a desert is water, and a measure to sufficiently secure water and supply the water is desired.
As conventional art, there is a method in which a water retention material is mixed with a dry land to adhere to roots of plants, and there are also the following techniques as preceding techniques.
Patent Literature 1 describes a method in which a hydrophobic layer composed of hydrophobic particles is provided in soil at a predetermined depth from the ground surface for controlling an amount of water in the soil. It provides a mechanism for controlling evaporation of water from desert soil.
In addition, Patent Literature 2 describes a soil block for potted plant cultivation that includes a water retaining layer, a hydrophobic layer above the water retaining layer, and a soil layer above the hydrophobic layer. Patent Literature 2 provides a soil block for potted plant cultivation that retains an appropriate amount of water for a long period of time and that allows easy water management, and a method for cultivating a potted plant by using the same.
Further, Patent Literature 3 describes an artificial soil structure that includes a water permeating layer in soil, a gravel layer present above or surrounding the water permeating layer, a hydrophobic layer that is present above the gravel layer and that is composed of hydrophobic particles, and an upper layer present above the hydrophobic layer. In Patent Literature 3, a specific combination of a water permeating layer and a hydrophobic layer is provided to a geological layer structure constituting soil, whereby necessary water is secured and efficiently supplied to the upper layer of the soil in which agricultural products are cultivated. By so doing, a soil environment suitable for plant cultivation is provided to drylands, such as desert, where farming previously could not be done. Sea water circulated to the water permeating layer is used to supply necessary water to the upper layer in which agricultural products grow.
Further, Patent Literature 4 describes an artificial water retaining soil structure that is composed of: a soil including a water retention agent; and a hydrophobic layer above the soil that is composed of hydrophobic particles. Patent Literature 4 provides an artificial water retaining soil structure that can mainly control evaporation of water in soil, a method for manufacturing the same, and a method concerning suppression of water evaporation in soil.